The field of the present disclosure relates generally to carbon nano-technology and, more specifically, to systems and methods of monitoring the structural integrity of a structure.
The fabrication of multi-layer laminate structures generally includes bonding layers of metallic (e.g., aluminum, titanium, or corrosion resistant steel (CRES)) and/or non-metallic (e.g., carbon fiber, boron, or fiberglass) reinforcement material together with a matrix material to form a rigid structure. The reinforcement material strengthens and stiffens the laminate structure, and the matrix material supports the reinforcement material after a curing process. Multi-layer laminate structures generally have a high strength-to-weight ratio and may be formed in a variety of shapes and sizes.
Recently, at least some known aircraft components have been fabricated from multi-layer laminate structures of non-metallic composite materials such as carbon-fiber-reinforced polymer (CFRP). The composite materials are used in combination with metallic materials, such as aluminum, titanium, and/or steel, to reduce the weight of the aircraft. As used herein, the term “metallic” may refer to a single metallic material or a metallic alloy material. Reducing the overall weight generally contributes to increasing the fuel efficiency of the aircraft.
However, common multi-layer laminate structures fabricated from CFRP may be susceptible to damage, such as the formation of micro-cracks and delamination of the structure during service. Known damage to such structures may be small and difficult to detect during scheduled maintenance. One known method of detecting structural defects in composite structures is to disperse carbon nanotubes in the polymer matrix used to form the structure. The carbon nanotubes form a conducting network of sensors that detect structural defects based on the piezoresistivity of the carbon nanotubes. Piezoresistivity refers generally to a change in the electrical resistivity of an electrically conductive material as mechanical stresses are induced thereto. As such, changes in the structural integrity of the composite structure may be detected by a change in the electrical resistivity of the polymer matrix containing the carbon nanotubes. However, it may be difficult to determine an exact location of structural defects when the carbon nanotubes are dispersed throughout the laminate structure.